Previous astronomical observations have detected high-energy gamma rays coming from the centre of our galaxy, and scientists have wondered where they came from.

"There has to be some sort of energetic particles buzzing around in the region in order to generate those very, very high energy light particles [gamma rays] that we detect from the region," says Crocker.

The black hole at the galaxy's centre is an obvious suspect. But how can it produce these high energy emissions?

Crocker and colleagues took their cue from what happens in particle accelerators, such as those at CERN, the European Organization for Nuclear Research facilities in Switzerland.

Experiments here show that high-energy gamma rays are produced by colliding high-energy protons (hydrogen nuclei), accelerated to almost the speed of light.

This produces particles called pions, the 'glue' that holds a nucleus together, and some of these tiny particles degrade into gamma rays.

Crocker and team reasoned that strong and chaotic magnetic fields, suspected to be at the rim of the black hole, could also accelerate protons.

They modelled this idea on computer and found that the accelerated protons bounce around and eventually escape into space.

About three light-years out from the black hole the high-energy protons smash into a cloud of hydrogen gas to produce gamma rays.

Astrophysicist Dr Zdenka Kuncic of the University of Sydney says it's a "fairly solid argument". But she emphasises a few problems, which the authors themselves acknowledge in their paper.

"They [Crocker and colleagues] are actually just testing one specific model, or one specific interpretation and others have been proposed," she says.

And Kuncic says telescopes can only locate the source of the gamma rays to an area with a five-light-year radius.

Since the black hole is a million times smaller than this, she says the gamma rays might not be coming from the black hole at all.

Another problem is the number of protons that are needed to produce the observed gamma rays is much higher than the number of protons that can be produced by known mechanisms for accelerating particles to high energies, says Kuncic.

Another particle accelerator?

This means that if Crocker and colleagues are right, then there must be a more efficient, yet-to-be-discovered mechanism that accelerates particles in space.

The protons produced at the centre of the Milky Way are accelerated to 100 trillion electronvolts (a measure of energy), much higher than what is possible on Earth.

For example, it is 18 times more energetic than the particles that will be produced by the proposed Large Hadron Collider in Switzerland.

The researchers suggest other black holes in the universe, which are much larger than the one in the Milky Way, may also act as particle accelerators, accelerating protons to much higher energies.